Tubular Cast On

[deosh]

Hello Gurus....

Starting a shrug that involves a tubular cast on as the base for the back edge (it's knit in one piece essentially, back to collar). Having a hard time with the pattern, which reads:

Cast on in scrap yarn using preferred method (calls for half the number req'd). Switch to working yarn and do required 4 rows of tubular cast on.

First row: K1, *yo, K1* repeat from * to * across, end K1
2nd row: K1, *Sl1 P with yarn in front, move yarn to back, knit next stitch (yo of previous row)*, repeat from * to * across, end K1.
Repeat 2nd row 2 more times following sense of the ribbing.

Problem is, I don't know what to do when I start my third row...I am looking at what appear to be 2 "purls" (the knit yo and the K1). To keep the sense of the ribbing, while following this pattern, I'd be slipping those 2 "purls", K1, etc.. Will I slip the last "purl" at the end of the third row as well?
I am so confused, I'm ready to use one of the other tubular cast on methods I've read about. Here's another question: if I use, say, the Italian method which involves casting on your required # of stitches right off, will this affect the end result significantly?

Attaching a photo of the garment, though it's a dark colour and a bit hard to make out. Thank you so much, in advance...